Assessments of Rhagoletis pomonella (Diptera: Tephritidae) infestation of temperate, tropical, and subtropical fruit in the field and laboratory in Washington State, U.S.

To understand the likelihood of any risk of apple maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), to domestic and foreign fruit export markets, knowledge of its host plant use is needed. Here, assessments of R. pomonella infestation of temperate, tropical, and subtropical fruit were made in the field and laboratory in Washington State, U.S. In field surveys in 2010– 2017 in central Washington, 6.7% of Crataegus douglasii and 6.1% of feral Malus domestica trees (both temperate plants) in fly-managed (insecticide- treated) sites were infested by larvae. In unmanaged sites, 54.1% of C. douglasii and 16.3% of feral M. domestica tree samples were infested. In field surveys of 36 types of temperate fruit in 2015–2018 in southwestern Washington, new host records for R. pomonella were one species and three hybrids of Crataegus, as well as Prunus domestica subsp. syriaca – all of which produced adult flies. In addition, Prunus avium was a new host record for Washington State, producing one adult fly. Prunus armeniaca x Prunus salicina and Vitis vinifera exposed to flies in the laboratory produced adult flies. Of 37 types of tropical and subtropical fruit hung in fly-infested M. domestica trees in southwestern Washington, only Mangifera indica produced puparia. Out of nine tropical and subtropical fruit types in laboratory tests, Musa acuminata x balbisiana produced puparia but no adult flies. Results provide a basis for further research and hypotheses concerning host use by R. pomonella and its potential impact on protecting both U.S. and tropical and subtropical fruit markets

Ammonium Carbonate Is More Attractive Than Apple and Hawthorn Fruit Volatile Lures to Rhagoletis pomonella (Diptera: Tephritidae) in Washington State

The apple maggot fly, Rhagoletis pomonella (Walsh), is an introduced, quarantine pest of apple (Malus domestica Borkhausen) in the Pacific Northwest of the United States. In the eastern United States where the fly is native, fruit volatiles have been reported to be more attractive than ammonia compounds to R. pomonella. However, the opposite may be true in the western United States. Here, we determined whether newly identified western apple and western hawthorn fruit volatiles are more attractive than ammonium carbonate (AC) to R. pomonella in apple, black hawthorn, and ornamental hawthorn trees in western Washington State. In all three host trees, sticky red sphere or yellow panel traps baited with AC generally caught more flies than traps baited with lures containing the four newly developed fruit blends (modified eastern apple, western apple, western ornamental hawthorn, and western black hawthorn) or two older blends (eastern apple and eastern downy hawthorn). Fruit volatiles also displayed more variation among trapping studies conducted at different sites, in different host trees, and across years than AC. The results imply that traps baited with AC represent the best approach to monitoring R. pomonella in Washington Stat

Hybridization and the Spread of the Apple Maggot Fly, Rhagoletis pomonella (Diptera: Tephritidae), in the Northwestern United States

Hybridization may be an important process interjecting variation into insect populations enabling host plant shifts and the origin of new economic pests. Here, we examine whether hybridization between the native snowberry-infesting fruit fly Rhagoletis zephyria (Snow) and the introduced quarantine pest R. pomonella (Walsh) is occurring and may aid the spread of the latter into more arid commercial apple-growing regions of central Washington state, USA. Results for 19 microsatellites implied hybridization occurring at a rate of 1.44% per generation between the species. However, there was no evidence for increased hybridization in central Washington. Allele frequencies for seven microsatellites in R. pomonella were more ‘R. zephyria-like’ in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria. However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA. Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population. The dynamics of hybridization are therefore complex and nuanced for R. pomonella, with various causes and factors, including introgression for a portion, but not all of the genome, potentially contributing to the pest insect\u27s spread

Geographic and ecological eimensions of host plant-associated genetic differentiation and speciation in the Rhagoletis cingulata (Diptera: Tephritidae) sibling species group

Ascertaining the causes of adaptive radiation is central to understanding how new species arise and come to vary with their resources. The ecological theory posits adaptive radiation via divergent natural selection associated with novel resource use; an alternative suggests character displacement following speciation in allopatry and then secondary contact of reproductively isolated but ecologically similar species. Discriminating between hypotheses, therefore, requires the establishment of a key role for ecological diversification in initiating speciation versus a secondary role in facilitating co-existence. Here, we characterize patterns of genetic variation and postzygotic reproductive isolation for tephritid fruit flies in the Rhagoletis cingulata sibling species group to assess the significance of ecology, geography, and non-adaptive processes for their divergence. Our results support the ecological theory: no evidence for intrinsic postzygotic reproductive isolation was found between two populations of allopatric species, while nuclear-encoded microsatellites implied strong ecologically based reproductive isolation among sympatric species infesting different host plants. Analysis of mitochondrial DNA suggested, however, that cytoplasmic-related reproductive isolation may also exist between two geographically isolated populations within R cingulata. Thus, ecology associated with sympatric host shifts and cytoplasmic effects possiblyFil: Doellman, Meredith M.. University of Notre Dame-Indiana; Estados UnidosFil: Schuler, Hannes. University Of Bozen-bolzano; ItaliaFil: Saint Jean, Gilbert. University of Notre Dame-Indiana; Estados UnidosFil: Hood, Glenn R.. Wane State University; Estados UnidosFil: Egan, Scott P.. Rice University; Estados UnidosFil: Powell, Thomas H. Q.. University of Binghamton; Estados UnidosFil: Glover, Mary M.. University of Notre Dame-Indiana; Estados UnidosFil: Bruzzese, Daniel J.. University of Notre Dame-Indiana; Estados UnidosFil: Smith, James J.. Michigan State University; Estados UnidosFil: Yee, Wee L.. United States Department of Agriculture. Agricultural Research Service; ArgentinaFil: Goughnour, Robert B.. Washington State University; Estados UnidosFil: Rull Gabayet, Juan Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Aluja, Martín. Instituto de Ecología A.c.; MéxicoFil: Feder, Jeffrey L.. University of Notre Dame-Indiana; Estados Unido

Hybridization and the Spread of the Apple Maggot Fly, Rhagoletis pomonella (Diptera: Tephritidae), in the Northwestern United States

Hybridization may be an important process interjecting variation into insect populations enabling host plant shifts and the origin of new economic pests. Here, we examine whether hybridization between the native snowberry-infesting fruit fly Rhagoletis zephyria (Snow) and the introduced quarantine pest R. pomonella (Walsh) is occurring and may aid the spread of the latter into more arid commercial apple-growing regions of central Washington state, USA. Results for 19 microsatellites implied hybridization occurring at a rate of 1.44% per generation between the species. However, there was no evidence for increased hybridization in central Washington. Allele frequencies for seven microsatellites in R. pomonella were more ‘R. zephyria-like’ in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria. However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA. Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population. The dynamics of hybridization are therefore complex and nuanced for R. pomonella, with various causes and factors, including introgression for a portion, but not all of the genome, potentially contributing to the pest insect\u27s spread

Table S1

Relative percentages of chemical compounds comprising the synthetic fruit volatile blends used in the study to test Rhagoletis pomonella fly behavior

Data from: A field test for host fruit odour discrimination and avoidance behaviour for Rhagoletis pomonella flies in the western United States

Prezygotic isolation due to habitat choice is important to many models of speciation-with-gene-flow. Habitat choice is usually thought to occur through positive preferences of organisms for particular environments. However, avoidance of non-natal environments may also play a role in choice and have repercussions for postzygotic isolation that preference does not. The recent host shift of Rhagoletis pomonella (Diptera: Tephritidae) from downy hawthorn, Crataegus mollis, to introduced apple, Malus domestica, in the eastern U.S. is a model for speciation-with-gene flow. However, the fly is also present in the western U.S. where it was likely introduced via infested apples < 60 years ago. R. pomonella now attacks two additional hawthorns in the West, the native C. douglasii (black hawthorn) and the introduced C. monogyna (English ornamental hawthorn). Flight tunnel tests have shown that western apple-, C. douglasii-, and C. monogyna-origin flies all positively orient to fruit volatile blends of their respective natal hosts in flight tunnel assays. Here, we show that these laboratory differences translate to nature through field trapping studies of flies in the state of Washington. Moreover, western R. pomonella display both positive orientation to their respective natal fruit volatiles and avoidance behaviour (negative orientation) to non-natal volatiles. Our results are consistent with the existence of behaviourally differentiated host races of R. pomonella in the West. In addition, the rapid evolution of avoidance behaviour appears to be a general phenomenon for R. pomonella during host shifts, as the eastern apple and downy hawthorn host races also are antagonized by non-natal fruit volatiles

Table S2

Behavioral responses of Rhagoletis pomonella flies from the western and eastern U.S. to synthetic host fruit volatile blends in flight tunnel assays

DEM Simulation of Frozen Granular Soils with High Ice Content

High volumetric ice content is one of the structural features of alpine permafrost. The mechanical properties of pure ice are very different from those of dry soil and as a consequence the mechanical properties of frozen soil are highly dependent on the ice content, as highlighted by triaxial experiments available in the literature. On the basis of existing data from experiments under different stress paths (axis-symmetric compression and extension), this paper presents a frozen soil model by using the particle-based discrete element method (DEM). In the model two groups of elements are used for representing soil particles and ice, and two separate sets of micromechanical parameters are calibrated and assigned to each group. Elements from the two groups are then mixed in different proportions in order to simulate the effect of ice content. A series of triaxial compression simulations are then performed and analysed